DNA replication proteins of E. coli and phage lambda have been purified and the reactions they catalyze are under study. Lambda replication in vivo requires two phage proteins, the O and P gene products, in addition to host proteins including dnaB, polC, dnaG, dnaZ, dnaJ, dnaK, grpD and grpE gene products. Of these proteins dnaB, dnaG, polC, dnaZ, and lambda P protein have been purified. Genetic results of others suggest that the lambda P protein functions cooperatively with E. coli dnaB, dnaJ, dnaK, grpD and grpE proteins. In vitro, lambda P protein forms a molecular complex with dnaB protein. Attempts are being made to isolate the lambda O protein and to reproduce the in vivo pathway of replication in vitro. The goal of these projects is to elucidate the molecular mechanisms by which DNA is replicated.